Real-time gas monitoring at the Tekke Hamam geothermal field (Western Anatolia, Turkey): an assessment in relation to local seismicity

This study presents the results of a real-time gas monitoring experiment conducted, via the use of a quadrupole mass spectrometer, in a mofette field within the Tekke Hamam geothermal site in western Anatolia (Turkey), a tectonically active region hosting several east-west trending grabens. The study is aimed to establish a baseline gas profile of the region. Within the framework of the experiment, gas compositions (CO2, N-2, O-2, H-2, H2S, CH4, He, and Ar) and flow rate of a mofette were monitored during two observation periods: November 2007-January 2008 and April-July 2008. During the course of monitoring, the major gas component was CO(2)with concentration changing around 96 volume percent. Other gases, from the most abundant to the least, were N-2, CH4, O-2, H2S, Ar, H-2, and He. The study produced a short-term, baseline gas profile of the region with daily/diurnal variations and temporal gas fluctuations appearing as instant signals. Although the temporal gas fluctuations did not reach the anomaly level (variations staying within the mean +/- 2 sigma), some of the variations in more than one parameter in the gas compositions (exceeding the mean +/- 1 sigma), accompanied by changes in the diurnal gas pulses lasting for long durations, were correlated with the seismic events selected according to the adopted seismic event elimination criteria. The variations were mainly attributed to changing gas mixing ratios in relation to porosity/permeability modifications possibly related to seismicity. Studies involving the continuous monitoring of meteorological parameters are necessary to assign these variations to geogenic events.